Receiver channel switch for object locators



Aug. 21,1951 w. A. HUBER ET AL ,5 ,6 v

RECEIVER CHANNEL SWITCH FOR OBJECT LOCATORS Filed March 12, 1943 I 4 Sheets-Sheet 1 REOEIVER\ I'- II Iz :IO

I FIG.I I3 Is I4 I5A I58 i MULTI- ii I VIBRATOR I AMPLIFIER AND AMPLIFIER I AMPLIFER q 5c I 29 v I I l 'AuToNIATIc ANTENNA I I TRACKER IsA PROPER I v A I I l 1 r 26 I I I SQUARE I I WAVE R I I I ANPLIPIE I :1 I AND R I mg I I INVERTE I 26A 26B I PLLI; I I' I:L

I1 METER IA-"ON AMPLIFIER RANGE ELE OR I I AND METER mm-H I SYNCHRO- l SCOPE soon: 25 NIZER I l :FIQA FISA! :ZZA J I I IBA I n ECHO E 24 2a MA TE L PHASE I I SELECTING v u I PULSE l- L J I8 I9 TRANSMITTER j INVENTOR WILLIAM A. HUBER WILLIAM r. POPE JR.

Aug. 21, 1951 w. A. HUBER m- AL 2,554,694

RECEIVER CHANNEL swncu FOR OBJECT LdcAToRs Filed March 12, 1943 4 Sheets-Sheet 3 INVENTORS WILLIAM A. HUBER BY WILLIAM T. P E JR.

ORNEY Aug. 21, 1951 w. A. HUBER El 1. 25,

RECEIVER CHANNEL SWITCH F OR OBJECT LOCATQRS Filed March 12, 1943 4 Sheet-Sheet 4 FIG. 4.

I 534 L A m \\\\\--E@ q an 512 V? z. 5i

ass so T0 POTENTIAL 523 souacs T 0 POWER SUPPLY ANTENNA ARRAY ANTENNA 53 TRACKING MOTOR TO GEAR o.c. VOLTAGE RANGE OSCILLOSCOPE SCREEN FIG.5

TRANSMITTER 1 PULSE HAIR-LINE AZIMUTH OR ELEVATION OSOILLOSCOPE SCREEN.

FIG. '0"- FIG. 8 i

INVENTORS WILLIAM A. HUBER ATTORNEY.

Patented 21, 1951 one RECEIVER CHANNEL SWITCH FOR OBJECT LOGATORS William A. Huber,

Neptune City, and William '1.

Pope, Jr., Asbury Park, N. 3., assignors to the United States of Secretary of War America as represented by the Application March 12, 1943, Serial No. 478,862

5 Claims.

(Granted under the act of March amended April 30, 1928; 370 0.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates object-detecting system.

In systems of this type, a pulse of radio-frequency energy is radiated by a highly directional antenna. If the transmitted waves strike an ob- Ject capable of reradiating these waves they will he reflected in part back to their source by this object. This echo pulse on its return to its source has suiilcient energy to produce an observable eflect in a suitable receiver located in the vicinity of the original source of these pulses. Generally the efiect consists of visual indications on a cathode-ray oscilloscope in a form of vertical peaks to a radio pulse-echo projecting upward from a horizontal base line.

These visual indicatio to ether with the positioning of antennae, are utilized for determining the location of the object.

A complete reliance by the operators of the radio systems of this type on the visual indications produced on the oscilloscope screen alone is not free of disadvantages. The vertical peaks produced by the echo signals may vary in their amplitude from one instant to another, because of the fluctuations in the intensity of the reflected signal, interference Si nals which may add to or subtract from the echo signals because of variations in the transmission medium, and because of other causes which need not be discussed here. Moreover, the signal pattern as it actually appears on the oscilloscope screen generally includes a large number of echo signals proper as well as a multitude of pulsating signals, commonly called noise or grass. Another factor which must be considered relates to the illumination generally found on the oscilloscope screen. This illumination is low if compared with daylight. and when the equipment is used in the daytime there is a very marked contrast in light due to quick changes from light to dark and vice The operating conditions outlined above make it very desirable that the systems of this type provide some additional indicating instrument which would track a single selected echo only, and would also be devoid of the disadvantages inherent in any oscilloscope system. Moreover, the operator's duties may be rendered even less burdensome and the accuracy of the entire system 3, 1883, as G. 757) considerably improved if the circuits of this single echo meter tracker are so constructed that they can perform a dual function: toprovide an indication of the degree and direction of antenna deflection from a single echo signal selected by the operator on the oscilloscope screen, and secondly, to provide suflicient power of right polarity for automatic antenna tracking of the selected echo.

One object of this invention, therefore, is to provide a new meter-tracker for the radio pulseecho object-detecting systems which gives the operator an even flow of data on the relative position of the single echo-producing object.

Another object of this invention is to provide motor driven equipment for automatic antenna tracking of that single object which is selected by the operator from a plurality of echoes appearing on the oscilloscope screen.

The novel features which we believe to be-characteristic of our invention are set forth with particularity in the appended claims. Our'invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings:

Fig. 1 is a block diagram of the receiver of the radio pulse-echo detecting system provided with our meter tracker and automatic tracker;

Fig. 2 is a more detailed diagram of the meter tracker alone, with the main components of the receiver and automatic antenna tracker omitted;

Fig. 3 is a schematic circuit diagram of the meter tracker Fig. 4 is a schematic circuit diagram of the automatic antenna tracker;

Figs. 5 to 8 show the oscilloscope screens as they appear at various stages of the operating cycle of the system.

Receiver Referring to Fig. 1, it shows one type of echo detecting system for which our meter and automatic tracking equipment is particularly adapted. As shown in the figure, a receiver I0 is connected to a directional antenna array l|--l2 which has a plurality of divergent, partially overlapping reception patterns, so that the intensity of signal in the channels I3-H is equal when the array is parallel to the wave front of the reflected signal, and unequal when there is a departure from the above parallelism. The antenna arrays of this type are known, and do not form a part of our invention; therefore, their description need not be given here. It should be stated, however, that out invention is not restricted to any particular antenna system, and will function with any type of directional antenna system which has at lest two divergent, partially overlapping reception patterns capable of producing two signals of equal or unequal intensity depending upon the orientation of the system with respect to the plane of the incoming signal wave front. This signal detecting system may be used either in determining azimuth or elevation of the object; as the two systems for determining these vectors are identical, only one of them is illustrated in Fig.1. These systems are known in the art as double-tracking systems.

One part of antenna signal is impressed on a radio-frequency amplifier l3, and another part of antenna signal is impressed on a complementary radio-frequency amplifier M, the two amplifiers forming two parallel channels of the receiver. The signals in these radio frequency channels will be composed of the main transmitted pulse, one or more echo signals, if there are any echo-producing objects within the antenna patterns, and of interference signals. This is illustrated in Fig. 5 which shows a range oscilloscope screen with a typical signal pattern as it appears on the screen. As stated above, the amplitude of the echo signals in these channels may or may not be equal, and this amplitude difference is utilized as a guide for proper orientation of the antenna array.

A typical single-echo signal pattern on the elevation or azimuth oscilloscope screens is shown in Figs. 7 and 8. Normally all signals appearing on the screen of the range oscilloscope also appear on the oscilloscope screens of the azimuth and the elevation channels; for the sake of simplicity only one selected echo signal is shown in Figs. 7 and 8. Fig. 7 shows the signal pattern when the images have unequal intensities, and Fig. 8 shows the same images when they are made equal by pointing the antenna arrays directly at the echo-producing object.

To produce these two independent images of the same echo signal on the screen of an oscilloscope ll, the amplifiers l3 and Il are keyed by a multivibrator I; which generates two square waves IS-A and l5B of the same frequency but 180 out of phase. These square waves key the amplifiers l3 and I4, and make them alternately conductive and non-conductive. The output signals of these amplifiers are shown at l3A and M-A, the highest peaks indicating the transmitted pulse, and the smaller peaksindieating the echoes. The receiver proper I6 is connected to the amplifiers l3-l4 on its input side and to the oscilloscopes l1 and on its output side. The oscilloscope I! may either be an azimuth or an elevation oscilloscope depending upon whether the antennae ll-I2 are azimuth or elevation antennae. The signals as they appear on the output side of receiver are shown at li-A; they'consist Of a series of signals first from one B. F. channel and then the other R. F. channel. The sweep voltage of oscilloscope I1 is under combined control of a master oscillator l8 and a phase shifter IS on one side, and a square wave lS-C generated by the multivibrator. Since the master oscillator is used for keying the transmitter 3|, the sweep circuits of the oscilloscopes I1 and 2| are in constant synchronism with the transmitted pulses. The square wave |5C is in phase with square wave l5A, and is utilized in the sweep circuit of oscilloscope I1 4 for a lateral shifting of the cathode-ray beam in synchronism with the keying of two R. F. channels. Accordingly, the signals shown at l6A appear as two laterally displaced images on the screen of oscilloscopes ll (see Figs. 7 and 8), the degree of lateral displacement being controlled by varying the amplitude of square wave l5C.

A range oscilloscope II is connected to the output of receiver I6 and to phase shifter IQ. Since this oscilloscope is not connected to multivibrator l5, its sweep circuit is controlled only by master oscillator It, and, as a consequence, there is no lateral displacement of the signals coming from channels I3 and I4, but they appear as a single retraced signal when the antennae are pointed directly at the object. This is shown in Figs. 5 and 6. When antenna is not pointed at the object, then the two signals appear in phase, but have different amplitudes.

The operation of the receiver is, briefly, as follows: If there is a plurality of echo-producing objects within the antennae field, their echoes will appear on the range, azimuth, and elevation oscilloscopes as a plurality of peaked signals. To determine the distance to any one of these objects, the range oscilloscope operator revolves a hand wheel of the phase shifter ll until the selected echo signal appears with its left edge under the hair line of the range oscilloscope 28, as shown in Figs. 5 and 6, where Fig. 5 shows the relative position of the signals with respect to the hair line before any echo signal has been selected, and Fig. 6 shows the same signals but with the echo signal I selected by the range oscilloscope operator. The phase shifter has a correctly calibrated dial which gives a range distance. Operation of the phase shifter I! also shifts the echo signals on the screen of the elevation and the azimuth oscilloscopes (only one is shown in Fig. l) and positions the echo signal selected by the range unit operator in the center of the screens of these oscilloscopes as shown in Figs. 7 and 8. The operators of the azimuth and elevation oscilloscopes operate the hand wheels which point their antenna systems directly at the object. This proper orientation of the antennae equalizes the amplitudes of the split-echo images on the oscilloscope screens as shown in Fig. 8, and furnishes the necessary angles for locating the object.

I are such that its output will be zero when the antennae are properly oriented with respect to the echo-producing object, and it will produce a proportional voltage signal of one polarity when an echo signal is stronger in the R. F. amplifier l3 than in the R. F. amplifier l4, and vice versa. Only one echo signal, selected by the range oscilloscope operator, can have any effect on our meter circuit, the remaining echo signals as well as the transmitted signal being all suppressed by the echo-selecting circuit.

Referring again to Fig. 1, the meter circuit 2| consists of an echo-selecting pulse generator 22, a square wave amplifier and inverter 25, both of which are connected to a meter amplifier and synchronizer 24. The output of the meter synchronizer 24 is connected to.a meter 2' and an automatic antenna tracker 29.

When the range oscilloscope operator operates the phase shifter IS in order to select an echo signal on his oscilloscope screen, he also selects that single echo in the'meter circuit, since the input of the echo-selecting pulse generator 22 is connected to the output of the phase shifter I9 by a. conductor 23. The period of the sinusoidal wave generated by the master oscillator I8 is many times longer than the duration of the transmitted pulse and the duration of the echo pulse, the latter two being substantially equal. It becomes necessary, therefore, to reshape the sinusoidal wave input in the echo-selecting pulse generator 22, so that the period of the pulse delivered by this unit is equal in width to the transmitted pulse. Moreover, this unit is equipped with a phase-shifting network for the initial phasing of the transmitter pulse with the meter circuit.-

With these requirements satisfied, the echo-selecting pulse generator delivers a strong positive pulse to the meter amplifier 24 which renders this amplifier conductive for only a short period of a single echo pulse selected by the range operator. All other signals are blocked.

The input t the meter amplifier 24 is connected to the output of the receiver I6 by a conductor 25. It will, therefore, receive signals from both radio channels I3 and I4. Since the function of the meter tracker is to indicate, by means of a meter, the difierence in signal strength in these two channels, it is necessary to separate the two channel signals, amplify them, and apply them to some form of a differential circuit. The separation of these signals is accomplished by means of an electronic switch within the meter amplifier 24. This switch, consisting of two thermionic tubes with parallel input circuits, is synchronized with the switching of the receiver channels by means of square-wave amplifier and inverter 20, the input of which is connected to the multivibrator I5 by a conductor 21. It will be recalled that the multivibrator I5 keys the R. F. channels I3 and M. The square-wave amplifier and inverter 26 amplifies the square-wave input, and transforms it into two square waves 180 out of phase with each other. One of these square waves is impressed on the grid of one tube, and the other square wave is impressed on the grid of the other tube of the electronic switch within the meter amplifier and synchronizer 24, which renders these tubes alternately conductive and nonconductive in synchronism with the antenna lobe switching. This synchronous switching accom plishes the separation of the two channel signals in the meter circuit, and these separated channel signals are subsequently utilized in a pulseaveraging circuit, the output of which is connected to a meter 28 and to an automatic antenna tracker 29.

A more detailed block diagram of our meter circuit 2| is shown in Fig. 2.

Detailed block diagram 0 meter circuit Referring to Fig. 2, the output of phase shifter I9, Fig. l, is connected by a conductor 23, Fig. 2, to echo-selecting pulse generator 22, and more particularly to a buffer amplifier 203 which acts as an impedance matching device and as an amplifier. Sinusoidal wave output of the buffer amimpressed on phase shifter 204 which is used for the initial phasing of the meter with the transmitter. The output of phase shifter 204 is connected to amplifier 205 which is used to further amplify the sinusoidal wave so as to impress a very strong grid signal on overdriven amplifier 206. Approximately square wave 206-A, appearing in the output of this amplifier, is impressed on pulse-shaping condenser-resistance network 201. An adjustable resistance element included in this multivibrator I5, as shown in Fig. 1.

network is used to control the width of the pulse impressed on the grid of the first pulse-shaping amplifier 208. Square wave 200-11 is transformed into two peaked pulses201-A of positive and negative value in the condenser-resistance network, and the positive peak of this pulse is amplified and slightly reshaped in the 1st, 2nd and 3rd pulseshaping amplifiers 200, 200 and'2I0, the output signal of the latter being a substantially square wave 2 I ll A, the duration of which is equal to the duration of the single-transmitted pulse or the echo pulse.

This square wave is impressed on mixer 2I2 in.

meter amplifier and synchronizer 24, and is utilized to unblock meter unit 24 only for the duration of this square-wave signal. Mixer 2I2 is also connected to the output of receiven I6, Fig. 1, but, out of a plurality of the transmitterecho signals impressed on it by the receiver, only one echo signal selected by the operator of phase shifter I9, Fig. 1, can get through, the remaining signals being blocked by a strong negative bias potential normally impressed on this unit. This bias potential is overcome by the strong positive signal 2I0A from 3rd pulse-shaping amplifier 2l0. Accordingly, the signals appearing in the output of the mixer will consist of a series of the same echo signal, first from one R. F. channel I2, and then from another channel I3. This is shown at 2I2A. The number of signals appearing in one series will depend on the frequency ratio of master oscillator i8 and multivibrator 85,, Fig. 1.

In order to separate the signals from these channels, the output of mixer 2 I2 is connected in parallel to channel separators 2 I3 and 2M, which are rendered alternately conductive and nonconductive by the square-wave amplifiers 2 I5 and 2I6 in a manner previously described in connection with the description of Fig. l.

Square-wave amplifiers 2 I5 and M 6, along with amplifier 2 I I and inverter 2 I8, form square wave amplifier and inverter unit 26. This square wave amplifier and inverter unit 26 is connected to The wave forms of these elements are shown in Fig. 2 and are self-explanatory.

The output of channel separators 2I3 and 2M are connected to channel signal amplifiers 2I0 and 220 which integrate the incoming pulses in the condenser-resistance networks, amplify the integrated signal, and impress it on differential meter circuit whose reading is zero when the output of elements 2I9 and 220 is equal, as previously described in this specification.

Schematic diagram of the meter circuit Referring to Fig. 3, the dotted lines designate the same three main elements 22, 20, and 26, shown in Figs. 1 and 2. The conductors 23, 25, and 21 connecting those elements to the receiver, also appear in all three figures.

Echo-selecting pulse generator (Fig. 3).-Referring to echo-selecting pulse generator 22, the sinusoidal wave from phase shifter I9 is impressed on the following circuit: conductor 23, condenser 30I, resistances 302, 303, ground at resistance 303, and to ground in the phase shifter. Bias on grids 304 and 3M, and the intensity of signal input are so adjusted that both stages of twin amplifier VI operates as substantially linear amplifiers. Plate 305 is coupled by condenser 308 to condenser-inductance combination 306, 301A which are tuned to the. sinusoidal wave produced by master oscillator I8, Fig. 1; this tuned circuit presents a high impedance to any harmonics which may appear in plate 309 circuit if tube VI accidentally becomes slightly overdriven. Inductance Ill-A forms the primary winding of transformer 301, secondary 301-B of which is grounded through center tap 399. Secondary 391-13 is connected to double-pole, double-throw switch 3" which is used to reverse the connections between the secondary and condenser-resistance combination 3ll-3l2. By varying resistance 3I2 it is possible to obtain a phase shift in the sinusoidal wave in the order of 170, and, by reversing switch 3l0, it is possible a shift the phase an additional 180. This phase shifter is used for proper initial phasing of meter circuit with the transmitted signal, as described more fully under Adjustment of Meter Tracker."

The phase shifter is connected to grid 3 of the second stage of twin amplifier VI through condenser 3" and grid resistor 315. This stage is also a linear amplifier, its output being coupled to grid 3I9 of the second twin amplifier V2 through condenser 3 l9 and grounded grid resistor 329. The input circuit of grid 3? is so adjusted that the average bias potential of this grid, with normal signal input, is equal to cut-ofi potential of this tube, and the input signal is such that the tube is driven .to saturation on positive halves of the sinusoidal wave. The shape of plate 322 output, therefore, has an approximate form shown at 322--A. Plate 322 is connected to a common +B supply through resistor 323, and to grid 324 input circuit comprising coupling condenser 325, variable resistance 326 and fixed resistance 321, the latter being connected to conductor 323 which impresses a normally negative cut-oil bias on grid 324. The time constant of this input circuit is such that wave form 322-A is transformed into a grid signal 329 having positive and negative peaked pulses. The width of this pulse may be controlled by adjusting variable resistance 329. The positive pulse on grid 324 overdrives the second stage of twin triode V2 so that it appears as a trapezoidal signal on grid 330 of the secondshaping amplifier tube V3. Plate 33| of the tube V2 is connected to +B supply through plate resistor 332 and conductor 333, and to grid 330 of tube V3 through coupling condenser 334. Grid 330 is grounded through grid resistor 335, the latter being instrumental in producing linear operation of tube V3. The second stage of tube V2, tubes V3, and V4 comprise three stages of condenser coupled overdriven pulse-shaping amplifiers which transform grid signal 329 into square positive voltage wave 333 in the cathode output circuit of tube V4. Plate 331 of tube V3 is connected to plate supply conductor 333 through plate resistor 338, and to grid 339 of tube V4.through coupling condenser 349. Grid 339 is normally biased to a cut-off potential through grid resistor 34! and conductor 342.

In order to secure an adjustable positive output signal in conductor 343 a potentiometer type of connection is employed between conductor 343 and cathode output resistor 344. Plate 345 is directly connected to a positive voltage supply through conductor 345; it is also connected to grounded conductor 343 by a by-pass condenser 341. All cathodes of the tubes used in the echoselecting pulse generator are directly connected to grounded conductor 349. The plate and bias voltage are furnished by bleeder resistor 349 which is connected across a filter circuit of an appropriate rectifier (not shown) furnishing the necessary power supply. The necessary con- 8 ductors for connecting different parts of bleeder resistor 349 with the corresponding conductors in the circuits are indicated by the same numerals.

From the description of the echo-selecting pulse generator 22, it follows that the sinusoidal wave 394A generated by master oscillator l3 and impressed on grid 394 in this unit, is transformed into a series of uniformly spaced rectangular pulses 339, the width of these pulses being equal to the width of the transmitted pulses and to the width of the individual echo signals. By varying potentiometer 329 setting, this pulse may be made wider or narrower than the transmitted or echo pulses, and, by varying conductor 343 connection on resistor 344, the amplitude of this pulse may be either increased or decreased. This amplitude is normally adjusted so as to slightly more than neutralize the negative bias applied to grid 390 of mixer tube VI in the meter circuit. Moreover, the phase of the rectangular pulses 336 may be shifted by varying potentiometer setting 3l2 approximately and an additional 180 by operating switch 319. The use of all adjustments outlined above is explained under Adjustment of the Meter Circuit, that is given subsequently in this specification.

Square wave amplifier and inverter (Fig. 3) The inverter is connected to a multivibrator 19 by conductor 21. coupling condensers 499, I and grid resistor 492. The input circuit from multivibrator, therefore, is: multivibrator l9, conductor 21 (Fig. 1) condenser 499, grid resistor 492, condenser 49!, to grounded terminals at inverter 29 and multivibrator l5. This input circuit is connected to control grid 493 of pentode V9, where the square wave is amplified and impressed on a second amplifier tube V9. With the connections as shown in this figure, cathode 499 is operated at a potential below ground, and plate 401 is connected through resistor 409 to ground. However, plate 401 may be connected to a higher potential point on bleeder 349, such as conductor 333, so that full available voltage is impressed on this plate. The output of V9 is connected to a twin triode VI9, the upper triode of which is coupled to the plate output of V9, and the lower triode of which is coupled to cathode resistor 405. With plate 491 grounded through resistor 409, a circuit through condenser 499 is as follows: grounded resistance 409, condenser 409, resistor 4l0, conductor 4I3, condenser I in the cathodescreen grid circuit of tube V9 and ground. when plate 491 is connected across full voltage supply, it becomes necessary to shunt the upper part of bleeder 349 with condenser M9 to avoid the appearance of the square wave in the bleeder. Tube VI9 is overdriven by the signal output of triode V9. Twin triode VI9 amplifies the square waves still further, and, since one of its grids is connected to plate 491 and another to cathode 499, the two square waves 4l4-'-A and 4i9A appearing in its plate outputs are 180 out of phase.

These square waves are used for commutating or keying electronic switch V9 in meter amplifier and synchronizer 24, and since they must produce negative grid pulses in this electronic switch, plates 4' and 4|! must be operated at ground potential which is the cathode potential in the electronic switch. The circuit of plate 414 is conductor 4", grid resistor'399, conductor 339 to ground, lower part of bleeder 349 to negative side of the bleeder, conductor 3, and cathode M1. The circuit of plate 4!! is the same as that of plate 4, but through conductor 413 and ad- Justable grid resistor 33!.

switch in the meter circuit is "9 The operation of electronic switch V6 will be explained more fully in connection with the description of meter circuit 24.

The squarewaves 4l4A and 4l5-A gener ated by unit 26 are obviously synchronous with the keying of radio channels l3 and I4, and the period of these waves is equal to the period of the waves generated by multivibrator l5. Accordingly, they will key the electronic switch in the meter circuit 24 synchronously with the keying of the radio channels.

Since the multivibrator I itself is capable of generating two square waves 180 out of phase, there is no absolute necessity for having unit 26. If this unit is eliminated, then the electronic connected directly to the multivibrator. The advantage of having an independent square wave inverter unit for the meter tracker resides in the fact that it makes this tracker an independent unit, which can be readily connected and disconnected in the field.

Meter amplifier and synchronizer (Fig. 3) Conductor25 and coupling condenser 352 connect grid 35! of mixer tube V5 to the output of the receiver l6. The signals impressed on this grid are shown at 35lA. Tube V5, as shown, is a pentagrid mixer amplifier, but any other suitable mixer tube or pentode may be used. Control grid 35| is grounded through grid resistor 353. This grid is biased by cathode resistor 354 connected between cathode 355 and ground conductor 356. Condenser 351 is a by-pass condenser. The second control grid 356 is biased to cut-oii potential by bleeder 349 to which it is connected by conductor 356 and grid resistor 359. Grid 356 is also connected to the source of the echo-selecting pulse 336 by conductor 343, and coupling condenser 366. Grid 356 normally blocks tube V5, and the positive signals from the transmitter are not sufliciently strong to overcome the blocking eifect of this grid. However, when echo-selecting pulse 336 is impressed on grid 256, its blocking eifect is neutralized for the duration of the selected pulse. The eiTect of this unblocking on the signals coming from the receiver becomes apparent if one compares the signals shown at l6-A with the signals shown at 368-369; only the highest echo signal has been selected in each channel, and the remaining two echo signals as well as the transmitted pulse have been blocked. The output of tube V5 i connected to cathode 362 of twin triode V6 by condenser 36L Since mixer tube V5 is normally non-conductive, the amplified echo signal 35lA appears as a very strong negative pulse at cathode 362 of twin amplifier V6; this cathode input signal renders either the left or the right side of V6 conductive, depending upon the signals impressed on the grids of this tube. Grids 363 and 364 of this twin triode are directly connected to plates 4 and M5 of twin triode Vl6 on one side, and to ground through grid rsistors 365 and 366, resistor 365 being adjustable for equalizing the signak on these grids. Two square-wave signals 4|4-A and 4I5A, which are 180 outof phase and which are synchronized with the alternate switching of R. F. channels l3 and I4, Fig. 1, are impressed on grids 363 and 364, which renders each of the two halves of twin triode V6 alternately non-conductive.

This synchronous blocking of twin triode V6 separates the signals from the two R. F. channels so' that echo signals 368 from R. F. channel l3 appear in plate circuit 316, and echosignals 369 appear in plate circuit 3". These signals offers a are shown at 316-A and 31f-A. Cathode 362 of tube V6 is connected to ground through resistor 312, and plates 316 and 3 are connected through resistors 313314, and 315-316 respectively, and then through resistor 315' to conductor 328 which is adjustably connected to bleeder 349 at a point whose potential is slightly below ground. Accordingly, when there is no signal impressed'on cathode 362, this cathode is at a higher potential than the plates, and the twin triode is non-conductive on both sides.

Referring to the plate circuits more in detail, plate 316 circuit is as follows: resistances 313, 314, potentiometer resistance 315', conductor 328, which connects this plate to bleeder 349 at a point which is below the ground potential on this bleeder. Similarly, plate 3" circuit is: resist ances 315, 316 potentiometer 315', and conductor 328. Both plate circuits are also connected to ground through potentiometer 315' and resistance 311, the latter resistance being connected to ground by conductor 356. Resistances 311 and 315' are thus connected across the entire negative plate potential impressed by bleeder 349 across conductor 326 and ground; by adjusting the potentiometer connection at 315', it is possible to vary the negative potential impressed on plates 316 and 3". This negative potential is so adjusted that it just suppresses that part of the amplified signal appearing across input resistor 312 which represents the positive excess of the signal on grid 356 in mixer tube V5 produced bythe echo-selecting wave 336.

As has been stated previously in connection with the operation of mixer tube V5, the amplitude of the echo-selecting pulse 336 is so adjusted that part of this pulse appears in the output circult of tube V5. Accordingly, the selected echo pulse per se is superimposed over that part of pulse 336 which is higher than the fixed bias potential impressed on grid 356. Since this transmitted part of pulse 336 would lower the sensitivity by charging integrating capacities 319 and the meter circuit connected to the output of this tube. Condenser 318 is a by-pass condenser which low impedance path from the plates output V6 to cathode resistor 312, so that this output signal does not appear in the resistances 315 and 311.

From the above description of the operation of tube V6 it follows that it acts as an electronic switch or an electronic commutator which receives a series of echo signals first from one radio channel, and then a series of the same echo signals from another radio channel. Tube V6, with the assistance of echo-selecting pulse generator 22, separates these two series of channel signals so that each series appears in an independent output circuit'after they pass through this tube. These signals, if the integrating eflect of the associated circuits is disregarded, would appear as shown at 316-A and 31IA.

Condensers 319 and 386 are connected to grids 38l and 362 respectively, on one side, and to ground on the other side. Since the junction point of resistors 316 and 314 is grounded through condensers 316, it follows that each of these condensers is connected directly across the plate output resistors in their respective channels. Ac-

cordingly, each condenser proportional to the average will bear a charge voltage drop in the plate resistor across which it is connected, and the voltage produced by this charge will b impressed on a balanced direct-current vacuum tube voltmeter V'I. Grids "I and 382 of tube VI, which is a twin triode tube, are directly connected tocondensers ill, I, and to resistors 315, I13. The resistors connections are adjustable so that the voltmeter input circuit may be so balanced that when the signal intensities in the two input channels are equal, the plate currents in twin triode V! are also equal. Cathode 388 is connected to a common cathode bias resistor 38!, the latter being connected on the other side to a conductor connecting resistances ill and 318. Condensers. I", 38., resistor 38!, and resistors in the plates of tube VG, are so chosen that the time constant of this circuit is relatively large, and the biasing of tube V! is fixed so that it acts as a linear amplifier of the signals appearing across the integrating condensers. The bias potential on grids 315', "I and 382 is not affected by adjustment of potentiometer 315' because cathode "I and grids Ill and 382 of tube V! are both returned to the arm of potentiometer 315'. Therefore, potentiometer 315' is used to adjust the negative bias potential on the plates of tube VI without affecting the bias on tube V1. Cathode! is at' a slightly lower potential than ground, since they must be directly connected to the output circuit of tube V6 in order to obtain direct current amplification in tube V1. The input circuit of tube V1 may be short-circuited by operating switch 386. The purpose of this switch will be explained later under "Adjustment of Meter Tracker. Plates 381, 388 are connected to a source of positive potential by conductor as through resistors 389, IN and 390, the latter resistor having apotentiometer type connection so that the plate currents can be made equal when no input signals are impressed on grids "I, 302.

Meter 392, which may be, for example, a high impedance zero center voltmeter, is connected across the output circuit of tube V1. External resistance as may be connected in series with this meter if it is desired to increase the impedance of the meter connection so that it will not produce a shunting effect in this output cirponents of the echo signal are separated and appear in the output circuit of the electronic switch as two independent series of signals. These signals, separated according to their derivative channels, are impressed on condensers I'll-ill. which perform the important integrating function before the signals are impressed on the meter itself. The time constants of the meter tracker circuit are of such value that an overwhelming majority of the echo signal fluctuations described in the beginning of this specification are completely damped. This results in a substantially smooth variation in meter reading when the selected echo-producing object is being tracked. The degree of this damping may be varied and made very high if desired. Moreover. since the damping or integrating of the components is accomplished after their separation by theelectronic switch, this damping is not accomplished at the expense of the average sensitivity of the meter circuit. This even flow of the orientation data is very desirable for an accurate. continuous tracking of the fast-moving objects. Meter tracking is less fatiguing on the operator since meter reading refers to the selected echosignal only, and all other extraneous signals which ordinarily appear on the oscilloscope screen are completely eliminated; moreover, there is no possibility of temporary blindness created by a sudden, extreme change between the illumination on the oscilloscope screen and daylight. The operator is allowed more freedom to move around than if he were looking into an oscilloscope hood. and, finally, the output of the meter tracker could be used .for automatic antenna tracking. as described later in this specification.

Adjustment 0/ meter tracker The transmitter II and receiver ll, Fig. l, are

I started and put in operation.

cult. This becomes especially desirable when the output circuit of tube V1 is utilized not only for meter tracking, but for automatic antenna tracking as well, as isthe case here. Conductors I95 and 386 are connected to the automaticv antenna tracking equipment shown in Fig. 4.

From the above description of the meter tracker it follows that when the integrating capacitors I19, 3" are equally charged, the meter tracker will read center scale zero. However, if one capacitor is charged more than the other, the meter will read to the left or to the rightof the zero center scale, depending upon the orientation of the antenna array with respect to the target. The center scale zero reading indicates that the amplitude of the echo signals in the twov Meter tracker 2i may or may not have a switch connecting it to the receiver. Fig. 2 shows three switches, 200, "I and lflgwhich connect meter. tracker to the receiver, but these switches are not essential and may be replaced with ordinary plug connections between receiver II and meter tracker 2 I. If the'meter is provided with the switches, they are closed, and the meter circuit adjustments are made'in the following order: The first meter tracker adjustment is concerned with .the equalization of the square-wave signals impressed on grids 363 and 3N of'tube VI, comprising the electronic switch. This adjustment is performed by connecting oscillompe deflection plates between grid and ground and observing the shape, width and amplitude of one square wave. The same procedure is used' in connection with grid 363, and the amplitude of the observed wave is adjusted by varying resistance OI! until the two waves have equal amplitudes.

The second adjustment is conoerned'with the adjustment of the grid bias potential on grid III of tube V5. It may be recalled "that this potential is adjusted'so that it is slightlyless but opposite in polarity to the potential impressed on, grid 350 of the same tube by square wave 330. The two potentials-may be compared by direct measurement of the negative bias potential with a D. C. voltmeter, and by measuring the second potential with a peak'voltag'e meter. and comparing the two readings. The peak voltmeter reading should be slightly higher than the reading obtained with the D. C. voltmeter and positive in polarity if it is not, then the position of conductor 358 on the bleeder is adjusted until this is the case. Another method of adjusting this blocking potential on grid 350 may be accomplished by connecting an oscilloscope in the output circuit of tube V5, impressing the maximum expected signal from receiver is on grid 35l, and adjusting the position of conductor 358 on bleeder 349 so that this signal just disappears on the oscilloscope screen.

The third adjustment consists of balancing meter centering resistance 390. Switch 386 is closed and the input circuit of twin triode V1 is thus short-circuited Meter-centering potentiometer connection at resistance 390 is then used to electrically center the meter. After centering the meter the switch is placed in the open, or operating position.

The next adjustment is concerned with the proper phasing of the meter with the transmitter channel, and more particularly, with the transmitted signal. Equipment in the transmitter and the receiver channels introduce difierent phase shifts, and these must be nullified by properly adjusting phase shifter 204, Fig. 2, or elements 3l2, 3l0, Fig. 3 in the meter circuit so that keying of the meter circuit by square wave 336 is in phase with the transmitted signal as it appears on grid 35! of mixer tube V5. This phasing adjustment is accomplished as follows: Phase shifter I 9 (Fig. 1) is adjusted so that the trans mitter pulse is under the hairline on all three oscilloscopes, i. e. range, elevation and azimuth oscilloscopes. The input circuit of tube V1 is unbalanced by sliding conductor 315-A up on resistance 315, and by sliding conductor 313-A up on resistance 313. This adjustment increases the signal on grid 38! by including the entire resistor 315 in the input circuit, and decreases the signal on grid 382 by completely eliminating resistor 313 from the input circuit of this tube. The receiver gain is now turned down far enough to eliminate all but the transmitted pulse from the receiver output. The phasing adjustment resistance 312 is then ad usted for maximum deflection on meter 392. When this is so, then the transmitted signal as it appears on grid 35l will be in phase with the keying wave 336 since the entire transmitted signal can get through mixture tube. V5 only when there is a complete phase coincidence between the two signals. During this adjustment it may be found that no proper phase relation ship can be obtained by adjusting resistor 3l2. If this happens, then it means that the units are more than 170 out of phase, and operation of phasing switch 310 may be necessary in order to obtain a greater phase shift from this unit.

Adjustment of plate bias potentiometer 315' is the next adjustment. Phase shifter I 9 is now adjusted so that no signal appears under the oscilloscope line. After this has been done the plate bias potentiometer 315' is adjusted so that meter 392 is just about ready to move oil the center zero position. This adjustment impresses a sufiiciently negative bias on plates 310 and 311 of tube V6 so as to suppress that part of echoselecting pulse 335 impressed on tube V5 which gets through this tube.

Balance of the input resistances 315 and 313 is the last adjustment. The receiver gain is now turned up to bring in the echoes. Phase shifter 19, Fig. 1 is adjusted to bring in under the range oscilloscope hairline an echo signal, and, by using the spread control (varying the amplitudeof square wave l5-C) and the resulting double images on the elevation and azimuth oscilloscopes as indicators, the antenna is oriented until the amplitudes of the signals are equal. The potentiometer arms 315-A and 313A are then set so as to include resistances 315 and 313 in the input circuits of grids 3!" and 382, i. e. they are adjusted for maximum signal input. If after this adjustment is made the meter does not read zero, one of the potentiometer settings is reduced until it does.

The meter tracker is now ready for operation.

The adjustments outlined above can be made out in the field, or on the bench, while the radio receiver is being aligned. Once the meter circuit is adjusted in connection with any particular transmitter-receiver combination, the meter circuit should normally remain in a balanced condition and ready for an instantaneous use on any subsequent occasions without any additional preliminary adjustments.

Summary of the operation of the meter tracker The operation of the meter tracker has been described in detail already; therefore, only a brief summary of its operation will be given here.

The meter is particularly adapted for use with pulse-echo systems which utilize the doubletracking method for obtaining the location of an object. Two series of the transmitted and the echo signals are impressed on the meter circuit, one series coming from one lobe of the antenna, and another series of signals from another lobe. These signals are shown at l3-A and I4''-A, Fig. 1. The signals from the two receiver channels are impressed on the meter amplifier and synchronizer circuit 24 where all signals except the selected echo signals are suppressed, as shown at 2|2A, Fig. 2. Because of the doubletracking method used at the receiver these selected echo signals appear in the meter circuit 24, Fig. 2, as a series of signals first from one antenna scanning channel, and then fromanother antenna scanning channel, as shown at 2l2-A, Fig. 2. These signals from different channels are separated by channel separators H3, 2, Fig. 2, and are utilized to operate a balanced direct current vacuum tube voltmeter 22! connected in its output circuit. This meter indicates the amount and the direction of deviation of the antenna array from the echo-producing object, and is used as a visual indicator for aiding in directing the azimuth or the elevation antenna arrays at the object.

Automatic antenna tracker The schematic diagram of the automatic .antenna tracker is shown in Fig. 4. Conductors 395 and 396, shown in Fig. 3 as being connected across the output circuit of the tube V1, also appear in Fig. 4. These conductors are connected to switches 50l-593 and 502-504. The action of these switches is such that when switches 53 and 502 are open, switches 503 and 504 are closed. and vice versa, and switches 503 and 504 must open before switches SM and 502 close. Switches SM and 502 are used to connect and disconnect the meter circuit to the automatic antenna tracker. Conductors 505 tentiometer arms which connect switches 533 and 504 to their respective potentiometers 501 and 508. These potentiometer arms are each connected to a set of adjustable springs-Mk5 and 5! 1-5 I 2 which normally keep the potentiomand 506 represent two p0 eter arms at those points which render grids I3 and ill of vacuum tubes VII and VI2 normally at zero-bias, or at slightly negative bias. A bleeder resistor I5 supplies plate potential for plates SIB and ill of tubes VII and VI2 and the bias potential for the potentiometers 501 and 508. The action of the above springs is such that irrespective of the position of the arms F506 when they are released by the operator after the manual operation of them, they always come back to the same positions on their respective potentiometers. These positions are adjusted so that there is an equal plate current in the tubes VII and VI2. The potentiometer arms are connected to a manually operated wheel 534 which operates them simultaneously but in the opposite directions, i. e. when arm 505 is moved to the negative end of potentiometer 501, arm 506 is moved to the positive end of potentiometer 5.8, and vice versa.

The input circuit of tubes VII and VI2 may be connected to the output of the meter circuit by closing switches Sill-502 and by opening switches 533-504. When this is done, the grid resistors SIB and SI! are connectedin parallel with meter 392, Fig. 3, and any direct current voltage which appears across meter 392 and resistance 393 also appear across grid resistors 5I8 and SIS. Cathodes 520 and HI of tetrodes VII and VI2 are connected to such a point on bleeder SIS which will furnish sufiicient cathode-to-plate potential for proper operation of the tetrodes. The screen grids 522 and 523 may be connected directly to the positive side of bleeder 5I5 without any resistance in their circuits. The plates of the tetrodes are connected to the difierential control field windings 524 and 525 of an "Amplidyne set 526, driven by a motor 521. Although the automatic antenna tracker is illustrated by way of example in connection with an "Amplidyne set, it should be understood by those skilled in the art that any other torque amplifying means may be used.

The output of the Amplidyne" set 526 is connected to a direct current motor 528 which is connected by shaft 529 with gear box 530, and the latter is connected through an appropriate shaft 3| or chain transmission with the antenna array 532. The same antenna array is shown in Fig. 1 at I I and I2. This array may be either an azimuth or an elevation array, the Amplidyne set connected to the azimuth receiver drives the azimuth antenna array, and an identical set connected to the elevation receiver drives the elevation antenna array. 1

The adjustment of the automatic antenna tracker, which is identical for the azimuth as well as the elevation antenna arrays, is as follows: the Amplidyne" set is started by closing a switch (not shown) to power supply of motor 521 which drives the "Amplidyne set. At this time switches ill-502 and 5II3504 are open. Before switches SUI-502 are closed the meter circuit must be balanced, as described under Adjustment of Meter Tracker, so that meter 392 in Fig. 3 reads zero with no signal impressed on its circuit. If there is a danger of sudden signals being impressed on the antenna arrays III2 shown in Fig. 1, switch 336, Fig. 3 may be closed so as to short-circuit the input into the meter circuit. Thus, with no signal impressed on conductors 335 and 396 from the meter circuit, switches ill-502 are closed after connecting tubes VII and VI2 to their power supplies. The output of tubes VII and VI2 is then adjusted at l0 potentiometer connection 533 so that antenna tracking motor 523 remains stationary. Switches SIN-502 are then opened, switches 503-!" closed, and the springs of the potentiometer arms 505-50 balanced so that motor 523 remains stationary. This correctly adjusts the automatic antenna-tracker for operation from the meter circuit shown in Fig. 3.

The actual operation of the systems of this kind discloses that there is ordinarily a plurality of. echo. signals in the antenna field so that the visual picture found on the range oscilloscope appears as it is shown in Fig. 5. This has been previously discussed under that section of this specification which deals with the Receiver. It has been also stated in that section of the specification that the range oscilloscope operator selects a single echo signal by turning the wheel of phase shifter I9, (Fig. 1) until the desired echo signal (echo #1, Fig. 5) is positioned either under or next to the hairline of the range oscilloscope, as shown in Fig. 6. This positions the same signal under the hair lines of the azimuth and the elevation oscilloscopes. When this is accomplished, the azimuth and the elevation oscilloscope operators must turn their respective antenna arrays quickly so that the amplitudes of the split images (Fig. 7) are equalized, as shown in Fig. 8.

From the above description of the operating cycle, which precedes the automatic antenna tracking, it follows that there are two distinct phases in the preliminary orientation of the system before the automatic tracker may be profitably connected ,to the system. The first phase consists of the selection of the desired echo signal by the range operator. The second phase consists of a quick orientation of the azimuth and elevation antenna arrays to equalize the split images. During the first phase the automatic tracker must remain disconnected, because shifting of the echo signals on the oscilloscope screens during the echo-selecting period may impose very strong loads on the "Amplidyne sets when the undesired echo si nals pass under the hair lines of the oscilloscopes and when they are impressed on the meter circuits. These strong loads would be transmitted to the antenna arrays in a form of greatly amplified torques and may produce a mechanical injury of the system. At this stage the metertracker circuit may remain connected without any injury to the meter 332, but switches 50 I-5Il2 must remain open.

During the second phase of the preliminary orientation of the system, the diflerence in the signal amplitudes (Fig. 7) may be so large that an immediate closing of the antenna tracker switches SUI-502 may again result in an unduly large mechanical stress imposed on the mechanical structure of the systems. To avoid this switches 503-504 are closed first, and the control wheel connected to the potentiometer arms 50L- turned from its normally neutral position in such a direction as to equalize the amplitude of the images on the oscilloscope screens, as shown in Fig. 8. When this control wheel is turned, the normal balanced condition of tubes VII and VI2 is destroyed, and if grid 5I3 is rendered more positive by shifting of the potentiometer arm 505 on potentiometer 501 toward the positive end of this potentiometer, then grid 5 is rendered negative by the simultaneous shifting of potentiometer arm 506 toward its negative end. This results in an increase in the plate current of tube VI I, and a decrease in the plate current of tube Vl2, with the corresponding changes in the currents carried by the difierential field windings 524 and 525 of the Amplidyne set 526. The amplified power generated by the Amplidyne" set is impressed on the antenna tracking motor 528, which turns the antenna array in the direction which points it directly at the echo-producing object through gear box 530 and shaft 53L With the antenna array pointed substantially at the target, switches 503-504 are opened and switches SUI-502 are closed. This last operation transfers the antenna-tracking control from the manually operated wheel connected to the arms 505506 to the completely automatic antenna tracking by connecting the Amplidyne unit to the output circuit of the meter-tracker unit. As has been described previously in this specification. the D. C. potentials appear across the resistances 389 and 39L Fig. 3, which are substantially proportional to the peak voltages of the images shown in Figs. 7 and 8. This same voltage is impressed on the D. C. linear amplifier VI l-VI 2,

field windings 524 and 525, and antenna tracking motor 528 in its amplified form, this motor turning the antenna array so that its plane is parallel to the wave front of the echo signal.

The automatic tracker may be disconnected at any time by opening switches 50l502.

From the above description of the automatic antenna tracker, one may very readily see that its operation is completely automatic when switches Sill-502 are closed, and the speed of antenna tracking motor 528 depends on the difference in the intensity of the echo signals derived through their respective channels. As this difierence in intensity increases, so does the speed of the motor increase. When switches 50I5D2 are open and switches 503504 are closed, it is possible to rotate the antenna array at any desired speed by manipulating the potentiometer arms 505-506. The greater is the unbalance created by shifting these arms from their normally neutral position, the greater is the speed of the antenna-tracking motor.

Although we have illustrated preferred forms for carrying out our present invention, it is to be understood that modifications are feasible and we do not intend to be limited except as set forth in the following claims.

What we claim is:

1. In a radio pulse-echo object-locating system capable of comparing components of an echo signal derived throughseparate receiving channels, means for suppressing all but the desired echo signal, and an electronic switch for separating the components of Said signal according to their derivative channels, said electronic switch comprising two triode units with a common cathode connection to ground through a cathode resistance, and a coupling means between said first means and said cathode resistance whereby said echo signal renders said cathode negative with respect to ground.

2. In a radio pulse-echo object-locating system capable of comparing the channel components of an echo signal derived through separate receiving channels as in claim 1, wherein said electronic switch further comprises two parallel output circuits connected to two plates of said triode units, and a source of potential intercomnesting said output circuits and. said cathode, the negative terminal of said source being connected to said output circuits, and the positive 18 terminal to said cathode, said source acting as a plate-biasing potential for said triode units.

In a radio pulse-echo object-locating system capable of comparing the channel components of connected to a source of periodically varyingpotential rendering each side of said triode units alternately conductive, whereby said channel components of said echo signal derived through one channel appear in one output circuit of said triode units, and said channel components of said echo signal derived through the other channel appear in the other output circuit of said triode units.

4. In a radio pulse-echo object-locating system capable of comparing components of an echo signal derived through separate receiving channels, means for suppressing all but the desired echo signals, and an electronic switch for separating the component of said signal according to their derivative channels, said electronic switch comprising two triode units with a common cathode connection to ground through a cathode resistance, a coupling means between said first means and said resistance, two ground-through: resistors control grids, and two sources of rectangular periodic voltage pulses out of phase with respect to each other and in phase with said components of said signal, one of said sources being connected to one of said grids and the other source being connected to the other grid, whereby said channel components of said echo signal derived through one channelappear'in one output circuit of said triode un-its,and said channel components'of said echo signal derived through the other channel appear in the other output circuit of said triode units.

5. An electronic switch comprising two triode units having a common cathode connection, two grids and two anodes, a resistor grounding said cathodes, a source of intelligence signals having two signal components, said source being connected to said cathodes, a resistance connected between ground and each of said grids, a source of rectangular waves, a first pushrpull amplifier connected to said source of rectangular waves said amplifier having first and second anodes, said first anode being metallically'connected to one grid and said secondanode otthe'other grid of said triode units, whereby jsaidiamplifier' renders said grids alternately negative with respect to said common cathode, an =-output resistor connected across the plates of -said triode units, the midpoint of said output'resistor; being connected to the negative end of a source of potential, the positive terminal of .said-source being connected to ground whereby said source negatively biases the plates of said triode'units with respect to its cathode, a secondfpush-pull amplifier, the grids of said second push-pull amplifier being metallically connected acrosssaid output resistance, and a connection between the cathodes of said second push-pull ampiifier and said mid-point on said output resistor, said rectangular waves alternately making one of said triode units non-responsive and the other responsive to said intelligence sig- 3 WILLIAM A. HUBER.

1 WILLIAM T. POPE, JR.

(References on following page) 19 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Wolf Aug. 29, 1933 Koch Feb. 6, 1940 Wa119.ce Feb. 23, 1943 Graham July 16, 1946 {0 Number Number 

